1. Field of the Invention
This invention relates to polymerizable resinous condensates and the thermosetting products thereof.
2. Description of the Prior Art
Polyester resins, as such are understood in the relevant art, include the class of oligomeric polyesterification products prepared by reacting a dicarboxylic acid or a diacid anhydride with a dihydric alcohol. Polyester resins having polymerizable unsaturation provided by employing an .alpha.,.beta.-ethylenically unsaturated dicarboxylic acid as all or part of the diacid component when crosslinked with a vinyl monomer, yield thermoset resinous compositions having widespread utility in the laminating, molding and related arts. Particular applications of the aforesaid thermoset products importantly include their use in the fabrication of automobile body parts, boat hulls and the like structural elements. While these products exhibit overall an exceptionally good balance of chemical and physical properties, their impact resistance and dimensional stability could desirably stand improvement.
It is known that a class of oligomeric condensates containing terminal acrylic groups, commonly referred to as "vinyl esters", can be converted to thermoset products having superior impact resistance. The vinyl esters are obtained by reacting an acrylic acid with the conventional epoxy resins thereby providing an acrylic acid capped oligomeric polyetherification condensate. It is not practical, however, to cap a hydroxyl terminated polyester in a similar manner inasmuch as the esterification reaction involved requires the use of elevated temperatures which preferentially promote the polymerization of the indicated vinyl acid.
Yet another area of prior art investigation directed to improving the properties of the thermoset products derived from unsaturated polyester resins has centered on the incorporation of urethane residues or linkages in the polyester backbone. Application of this technology, however, has been essentially confined to the surface coating field rather than in the area concerned with molded compositions.